Preparation of improved motor fuels containing furan antiknocks

ABSTRACT

The octane rating of gasoline alkylate may be improved by separating therefrom 2,4- and 2,5-dimethylhexanes (&#39;&#39;&#39;&#39;DMH&#39;&#39;&#39;&#39;) and subjecting said DMH to the following combination of steps: (1) oxidizing the DMH to form the corresponding hydroperoxides; (2) reacting of the hydroperoxides with propylene to yield the corresponding diols plus propylene oxide; and (3) dehydrating of the diols to produce 2,2,5,5-tetramethyltetrahydrofuran (&#39;&#39;&#39;&#39;TMTHF&#39;&#39;&#39;&#39;), which product is then added to the gasoline alkylate, thereby improving its octane rating. In addition, valuable propylene oxide is recovered as a by-product.

nited States Patent 1 Stearns et a1.

i 1 PREPARATION OF IMPROVED MOTOR FUELS CONTAINING FURAN ANTIKNOCKS [75] Inventors: Richard S. Stearns, Malvern, Pa.;

Robert M. Thompson, Wilmington, Del.

[52] US. Cl ..44/63;252/386;260/346.1 R

[51] Int. Cl. COIL 1/14 158] Field of Search 44/63; 252/386; 260/346.1 R

{56] References Cited UNITED STATES PATENTS 2,321,311 6/1943 Mottlau et a1. 44/63 2.650.236 8/1953 Condon et a1. .1 260/346.1 R

2,870.214 l/l959 260/3461 R X 3.318.916 5/1967 Leonard 260/3461 R OTHER PUBLICATIONS Unzelman et a1, Are There Substitutes for Lead An- 1 1 Sept. 30, 11975 tiKnocl s? May 14, 1971, p. 888, AH Div. of Ref. Proceedings.

Primary Examiner-Delbert E Gantz Assistant E.\'uminerAndrew H. Metz Attorney, Agent, or Firm-George L. Church; Donald R. Johnson; Stanford M. Back [57] ABSTRACT The octane rating of gasoline alkylate may be improved by separating therefrom 2,4- and 2,5- climethylhexanes (DMH) and subjecting saidDMl-l to the following combination of steps: (1) oxidizing the DMH to form the corresponding hydroperoxides; (2) reacting of the hydroperoxides with propylene to yield the corresponding diols plus propylene oxide; and (3) dehydrating of the diols to produce 2,25,5- tetramethyltetrahydrofuran (TMTHF), which prod uct is then added to the gasoline alkylate, thereby improving its octane rating. 111 addition, valuable propylene oxide is recovered as a by-product.

14 Claims, N0 Drawings IREPARATION OF IMPROVED MOTOR FUELS CONTAINING FURAN ANTIKNOCKS BACKGROUND OF THE INVENTION This invention relates to a novel method for improving the octane rating of motor fuels. -More particularly, this invention relates to a novel composition and a multi-step process for preparing the same by converting dimethylhexanes obtained from gasoline alkylate to 2,- 2,5,5-tetramethyltetrahydrofuran, and returning said tetrahydrofuran to the gasoline alkylate in order to upgrade the same.

It is known that the presence of-dimethylhexanes in motor fuel alkylate is detrimental to its octane rating, as demonstrated by the 'fact that their'removal im proves its octane number by about two units. Removal of these compounds is alone not a satisfactory answer to this problem since the cost of the alkylate is increased by these processing steps, which cost is not offset by the value of the dimethylhexanes (DMH) in their recovered state.

Accordingly, development of amethod whereby the recovered DMH can be converted to a more valuable product, and particularly one which when added to the gasoline alkylate would increase its octane number, would be highly advantageous to the motor fuel art.

SUMMARY OF THE INVENTION In accordance with the present invention, it has been found that dimeth'ylhexanes recovered from conventional gasoline alkylates may readily be converted to the corresponding 2,2,5,5-tetramethyltetrahydrofuran, a compound which is known to increase the octane number of motor fuels. As a by-product of this process there is also recovered propylene oxides, or like olefin oxide depending upon the olefin reactant selected.

Thus, in accordance with this process there is carried out the following combination of steps:

1. a gasoline alkylate, i.e. a C -C alkylate, boiling in the range of from about 80 to 270F is distilled in order to recover 2,4 and 2,5-DMH; i

2. the DMH mixture is then oxidized with oxygen to form the corresponding 24- and 2,5-DMH hydroperoxides; i i

3. the peroxides thus obtained are reacted with a C ,C mono olefin to yield the corresponding DMH alcohol together with the corresponding olefin epoxide; 1

4. the DMH alcohol is dehydrated to produce 2,2,5,-

5-tetramethyltetrahydrofuran which is added to the alkylate. 1

DETAILED DESCRIPTION OF THE INVENTION In the firststep, a gasoline alkylate containing from about 6 to 8 percent by volume of 2,4- and/or 2,5- DMI-Is is distilled in a conventional manner, i.e. at a temperature of'about 228 to 230] in order to recover the DMH compounds. Desirably, as much DMH should be removed as is practicable, and in any event the remaining gasoline alkylate should contain not more than about 2 percent residual DMH. The gasoline alkylate charge stock to which the process generally pertains is that alkylate containing C -C hydrocarbons which boils in the range of from about 80 to 270F, and which is conventionally obtained by sulfuric acid or hydrofluoric acid alkylation.

The DMH mixture recovered therefrom is then oxidized in a known manner to produce the corresponding dihydroperoxides. This is conveniently achieved by oxidizing the DMH with oxygen at temperatures of about 235 to 290F., preferably about 240 to 280F, with low conversions per pass, i.e. about 15 to 25 percent per pass, and preferably about 20 percent, using no catalysts, but employing a peroxide or hydroperoxide initiator, such as dimethylhexyl hydroperoxide itself.

The dihydroperoxides thus obtained may then be reacted with a C;,C,, monoolefin, preferably propylene, to yield the corresponding DMH diol and olefin. oxide, such as propylene oxide. This epoxidation reaction is desirably carried out in accordance with the method described in J. Org. Chem. 35, p. 1839 (1970), i.e. with an excess of olefin over hydroperoxide, desirably in a mole ratio of about 3:1 to 15:1 of olefin to hydroperoxide, and preferably about 2:1, using a catalyst such as molybdenum hexacarbonyl at temperatures of from about to 95C, preferably at about to C. The catalyst should be present in amounts of about 4X 10 to l l0 moles per 0.5 mole of olefin. The product mixture when, e .g., propylene is employed as the olefin, comprises 2,4 and 2,5-DMI-I diol and propylene oxide,

which mixture is conveniently separated by distillation.

In the final step of the process the dimethylhexane diols are dehydrated to form 2,2,5,5-tetramethyltetrahydrofuran and water. This dehydration is readily achieved by contacting the diols with a catalyst such as aniline hydrobromide, at temperatures of about to C and recovering the TMTI-IF. The catalyst is generally employed in amounts of about 0.1 g. per mole of diol.

The T'MTI-IF thus obtained is then blended with the original gasoline alkylate from which the DMH had been removed to obtain a gasoline composition containing at least about 1 percent by volume of said TMTI-IF, preferably about 1.5 to 3.0 percent, and not more than about 2 percent unreacted DMH. When compared with the octane number of the original alkylate containing the 2,4- and/or 2,5-DMH, the overall effect of removing these latter compounds and converting them to TMTI-IF is to raise the octane number of the gasoline alkylate by a total of about 33.5 units. It will be understood, of course, that additional furan obtained from sources other than the original hexanes may also be employed toincrease the furan content of the alkylate if so desired.

In a further embodiment of this invention, it is also contemplated that the DMH hydroperoxides described above may themselves be used as octane improvers.

. 7 That is to say, these hydroperoxides are also able to in- EXAMPLE 1 Distillation of Sulfuric Acid Alkylate Product One gallon of gasoline alkylate obtained from conventional sulfuric acid alkylation, and containing about 7 percent by volume of a mixture of 2,4- and 2,5-

dimethylhexane was distilled on a Podbilniak still with a 25 mm X36 inch column containing heli-grid packing and an efficiency of 30 plates at a 30 to 1 reflux ratio. A hydrocarbon fraction boiling between 213 to 233F, and weighing 160 grams, was isolated. VPC analysis showed this fraction to contain 47 percent 2,5- dimethylhexanc, 28 percent 2,4dimethylhcxane, together with 16 percent 2,2,3-trimethylpentanc and some higher octane alkylates.

EXAMPLE 2 Oxidation of the 2l3233F Distillate Fraction In an apparatus similar to that described by F. F.

Rust, J, Am. Chem. Soc., 79, 4000 (1957), oxygen was EXAMPLE 3 Epoxidation of Propylene Using Oxidized Alkylate The dihydroperoxides were charged in a 1 liter Parr reactor, along with 0.1 g. of Mo(CO) and 44 g. of propylene percent excess). The mixture was heated with stirring to 110C. After 1 hour the reaction mixture was cooled to room temperature and the product analyzed for hydroperoxide conversion and epoxide formation by VPC. There was a 97 percent conversion of the hydroperoxides to 2,4- and 2,5-dimethylhexane diols; 48 g. of propylene oxides was recovered by distillation at low temperatures in vacuo and washed with thiosulfate solution to remove any traces of hydroperoxide.

EXAMPLE 4 Dehydration of the 2,4-Dimethylhexane-2,4-diol and 2,5Dimethylhexane-2,5-diol The residue comprising the DMH diols was distilled in the presence of aniline hydrobromide. 2.2,5,5- tetramethyltetrahydrofuran began forming slowly at 111.5C and continued until the temperature reached 125C; 52.0 g. of the TMTHF derivative was obtained.

EXAMPLE 5 Blending of 2,2,5,5-Tetramethyltetrahydrofuran and Residue Hydrocarbon in the Original Alkylate The 52 g. of TMTHF and the 100 g. of the hydrocarbon fraction from the oxidation step were combined and blended with the original alkylate from which it was obtained. The blended material was then tested for anti-knock characteristics. It was found to have an octane rating of 99.2, 3.3 numbers over the original of 95.9.

What is claimed is:

l. A process for improving the octane rating of a gasoline alkylate containing at least 6 percent by weight of a mixture of 2.4- and 2,5dimethylhexanes which comprises the steps of:

a. separating at least about 4 percent of said dimethylhexanes from said alkylate;

b. oxidizing the dimethylhexanes with oxygen to form the corresponding 2,4- and 2.5-dimethylhexane dihydroperoxides;

c. reacting said hydroperoxides with a C --C monoolefin to form a mixture of the corresponding dimethylhexane diols and olefin oxide, and recovering said olefin oxide from said mixture;

(:1. dehydrating said dimethylhexane diols to form 2,2-

,5,S-tetramethyltetrahydrofuran; and

e. combining said tctrahydrofuran with said gasoline alkylate from which the dimethylhexanes had been removed.

2. The process according to claim 1 wherein the monoolefin is propylene and the recovered olefin oxide is propylene oxide.

3. The process according to claim 1 wherein the mole ratio of olefin to hydroperoxide is about 3:1 to 1.521.

4. The process according to claim 1 wherein the reac tion of the olefin with the hydroperoxide is carried out in the presence of a catalyst.

5. The process according to claim 4 wherein the catalyst is Mo(CO) 6. The process according to claim 1 wherein the dimethylhexane diols are dehydrated in the presence of a dehydration catalyst.

7. The process according to claim 6 wherein the catalyst is aniline hydrobromide.

8. A process for the preparation of 2,255- tetramethyltetrahydrofuran which comprises the steps of:

a. oxidizing 2,4- and 2,5-dimethylhexane with oxygen to form 2,4- and 2,5-dimethylhexanedihydroperoxide;

b. reacting said hydroperoxides with a C,,C monoolefin to form a mixture of the corresponding dimethylhexane diols and olefin oxide, and recovering the olefin oxide from said mixture;

0. dehydrating said dimethylhexane diols to form 2,2-

,5,5-tetramethyltetrahydrofuran.

9. The process according to claim 8 wherein the monoolefin is propylene and the recovered olefin oxide I is propylene oxide.

10. The process according to claim 8 wherein the mole ratio of olefin to dihydroperoxide is about 3:1 to

11. The process according to claim 8 wherein the reaction of the olefin with the hydroperoxide is carried out in the presence of a catalyst.

12. The process according to claim 8 wherein the catalyst is Mo(CO) 13. The process according to claim 8 wherein the dimethylhexanc diols are dehydrated in the presence of a dehydration catalyst.

14. The process according to claim 8 wherein the catalyst is aniline hydrobromide. 

1. A PROCESS FOR IMPROVING THE OCTANE RATING OF A GASOLINE ALKYLATE CONTAINING AT LEAST 6 PERCENT BY WEIGHT OF A MIXTURE OF 2,4 AND 2, 5-DIMETHYLHEXANES WHICH COMPRISES THE STEPS OF: A SEPARATING AT LEAST ABOUT 4 PERCENT OF SAID DIMETHYLHEXANES FROM SAID ALKYLATE, B. OXIDIZING THE DIMETYLHEXANES WITH OXYGEN TO FROM THE CORRESPONDING 2,4- AND 2,5-DIMETHYLHEXANE DIHYDROPEROXIDES, C. REACTING SAID HYDROPEROXIDES WITH A C3-C8 MONOOLEFIN TO FORM A MIXTURE OF THE CORRESPONDING DIMETHYLHEXANE DIOLS AND OLEFIN OXIDE AND RECOVERING SAID OLEFIN OXIDE FROM SAID MIXTURE, D. DEHYDRATING SAID DIMETHYLHEXANE DIOLS TO FORM 2,2,5,5TETRAMETHYLTETRAHYDROFURAN, AND E. COMBINING SAID TETRAHYDROFURAN WITH SAID GASOLINE ALKYLATE FROM WHICH THE DIMETHYLHEXANES HAS BEEN REMOVED
 2. The process according to claim 1 wherein the monoolefin is propylene and the recovered olefin oxide is propylene oxide.
 3. The process according to claim 1 wherein the mole ratio of olefin to hydroperoxide is about 3:1 to 1.5:1.
 4. The process according to claim 1 wherein the reaction of the olefin with the hydroperoxide is carried out in the presence of a catalyst.
 5. The process according to claim 4 wherein the catalyst is Mo(CO)6.
 6. The process according to claim 1 wherein the dimethylhexane diols are dehydrated in the presence of a dehydration catalyst.
 7. The process according to claim 6 wherein the catalyst is aniline hydrobromide.
 8. A PROCESS FOR THE PREPARATION OF 2,2,5,5-TETRAMETHYLTETRAHYDROFURAN WHICH COMPRISES THE STEPS OF: A. OXIDIZING 2,4- AND 2,5-DIMETHYLHEXANES WITH OXYGEN TO FORM 2,4- AND 2,5-DIMETHYLHEXANEDIHYDROPEROXIDE B. REACTING SAID HYDROPEROXIDES WITH A C3-C8 MONOOLEFIN TO FORM A MITURE OF THE CORRESPONDING DIMETHYLHEXANE DIOLS AND OLEFIN OXIDE AND RECOVERING THE OLEFIN OXIDE FROM SAID MIXTURE, C. DEHYDRATING SAID DEMETHYLHEXANE DIOLS TO FORM 2,2,5,5TETRAMETHYLTETRAHYDROFURAN
 9. The process according to claim 8 wherein the monoolefin is propylene and the recovered olefin oxide is propylene oxide.
 10. The process according to claim 8 wherein the mole ratio of olefin to dihydroperoxide is about 3:1 to 1.5:1.
 11. The process according to claim 8 wherein the reaction of the olefin with the hydroperoxide is carried out in the presence of a catalyst.
 12. The process according to claim 8 wherein the catalyst is Mo(CO)6.
 13. The process according to claim 8 wherein the dimethylhexane diols are dehydrated in the presence of a dehydration catalyst.
 14. The process according to claim 8 wherein the catalyst is aniline hydrobromide. 